1. Field of the Invention
The present invention relates to fiber optic gyroscopes and more particularly to compensation of thermally-induced drift rate errors in fiber optic gyroscopes.
2. Description of the Prior Art
Various types of sensors (angular position indicators and rate gyros) can exhibit significant temperature sensitivity to either temperature levels or rates of temperature change. In the search for instruments of greater accuracy, it has become necessary to either compensate for the resulting thermally-induced errors or to use heaters to provide a constant sensor temperature. Although heaters are used successfully to provide thermal control, they require additional power, an electronic controller, and result in higher average sensor operating temperatures.
The output of sensors that exhibit temperature level sensitivity, e.g., a predictable change in bias over temperature, can be readily corrected by means of a simple polynomial in temperature whose coefficients are determined by test, and whose value can be based on the output of an appropriately placed thermistor. However, compensation for sensors such as the fiber optic gyroscope (FOG) that exhibit sensitivity to small rates of temperature change is more difficult to achieve since the errors are not simple functions of temperature.
Electrolytic level sensors and plastic gyros also fall into this category. In the case of the level sensor, temperature measurement at the instrument was considered infeasible, and in the case of the plastic gyro, erratic thermal behavior precluded the development of a practical scheme of compensation. It should be noted that although the level sensor was thermally isolated, the electrolyte in the glass tube still exhibited erratic behavior because of the heat generated within the electrolyte itself. Erratic thermal behavior of the plastic gyro was attributed to the inherently low thermal conductivity of the plastic material used in its construction.
It is an object of the present invention to provide a means of correcting for sensor errors caused by thermal effects without the use of heaters and associated control electronics.